The present invention is directed to a continuous liquid phase hydroprocessing process, apparatus and process control systems, wherein the need to circulate hydrogen gas through the catalyst is eliminated. This is accomplished by mixing and/or flashing the hydrogen and the oil to be treated in the presence of a solvent or diluent in which the hydrogen solubility is high relative to the oil feed. The present invention is also directed to hydrocracking, hydroisomerization and hydrodemetalization.
In hydroprocessing, which includes hydrotreating, hydrofinishing, hydrorefining and hydrocracking, a catalyst is used for reacting hydrogen with a petroleum fraction, distillates, resids, or other chemicals, for the purpose of saturating or removing sulfur, nitrogen, oxygen, metals or other contaminants, or for molecular weight reduction (cracking). Catalysts having special surface properties are required in order to provide the necessary activity to accomplish the desired reaction(s).
In conventional hydroprocessing it is necessary to transfer hydrogen from a vapor phase into the liquid phase where it will be available to react with a petroleum molecule at the surface of the catalyst. This is accomplished by circulating very large volumes of hydrogen gas and the oil through a catalyst bed. The oil and the hydrogen flow through the bed and the hydrogen is absorbed into a thin film of oil that is distributed over the catalyst. Because the amount of hydrogen required can be large, 1000 to 5000 SCF/bbl of liquid, the reactors are very large and can operate at severe conditions, from a few hundred psi to as much as 5000 psi, and temperatures from around 400° F.-900° F.
The temperature inside the reactor is difficult to control in conventional systems. The temperature of the oil and hydrogen feed in the reactor can be controlled; however, once the feed is inside the reactor, there no adjustments to the system that can raise or lower the temperature of the oil/hydrogen mixture. Any changes in the reactor temperature must be accomplished through an outside source. As a result, conventional systems often inject cold hydrogen into the reactor if it becomes too hot. This method of cooling a reactor is expensive and is a potential safety risk.
While controlling the temperature of the reactor is often a difficult task in conventional systems, controlling the pressure of the hydroprocessing system is a much easier task. Pressure control systems are used to monitor the pressure of the system, release pressure through a valve if the pressure becomes too great, and to increase the pressure of the system if the pressure becomes too low. A pressure control system cannot be used to control the pressure on a single hydroprocessing reactor; however, this is of no serious consequence and instead pressure is maintained on the entire system, not on individual reactors.
One of the biggest problems with hydroprocessing is catalyst coking. Coking occurs when hydrocarbon molecules become too hot in an environment where the amount of hydrogen available is insufficient. The molecule cracks to the point that it forms coke, a carbonaceous residue. Cracking can take place on the surface of the catalyst, leading to coke formation and deactivation of the catalyst.
A conventional system for processing is shown in U.S. Pat. No. 4,698,147, issued to McConaghy, Jr. on Oct. 6, 1987, which discloses a SHORT RESIDENCE TIME HYDROGEN DONOR DILUENT CRACKING PROCESS. McConaghy '147 mixes the input flow with a donor diluent to supply the hydrogen for the cracking process. After the cracking process, the mixture is separated into product and spent diluent, and the spent diluent is regenerated by partial hydrogenation and returned to the input flow for the cracking step. Note that McConaghy '147 substantially changes the chemical nature of the donor diluent during the process in order to release the hydrogen necessary for cracking. Also, the McConaghy '147 process is limited by upper temperature restraints due to coil coking, and increased light gas production, which sets an economically imposed limit on the maximum cracking temperature of the process.
U.S. Pat. No. 4,857,168, issued to Kubo et al. on Aug. 15, 1989, discloses a METHOD FOR HYDROCRACKING HEAVY FRACTION OIL. Kubo '168 uses both a donor diluent and hydrogen gas to supply the hydrogen for the catalyst enhanced cracking process. Kubo '168 discloses that a proper supply of heavy fraction oil, donor solvent, hydrogen gas, and catalyst will limit the formation of coke on the catalyst, and the coke formation may be substantially or completely eliminated. Kubo '168 requires a cracking reactor with catalyst and a separate hydrogenating reactor with catalyst. Kubo '168 also relies on the breakdown of the donor diluent for supply hydrogen in the reaction process.
U.S. Pat. No. 5,164,074, issued to Houghton on Nov. 17, 1992, shows a HYDRODESULFURIZATION PRESSURE CONTROL apparatus for controlling pressure in a combination hydrodesulfurization and reforming process wherein the pressure of a hydrogen-rich gas source from the reforming process is adjusted by coordinately manipulating a vent control valve for the reforming process in a manner that insures maximum utilization of available hydrogen for desulfurization before any of the hydrogen from the reforming process is vented through its own vent valve.
U.S. Pat. No. 4,761,513, issued to Steacy on Aug. 2, 1988, shows a TEMPERATURE CONTROL FOR AROMATIC ALKYLATION PROCESS. The temperature control is a quench system that uses a methylating agent as a quench medium that is introduced between sequential reaction zones in a reactor. The proportion of vapor phase and liquid phase methanol is adjusted to control the enthalpy of the methylating agent and provide temperature reduction by the vaporization of the liquid component of the methylating agent.